1. Field of the Invention
The present invention relates to particles, particularly small particles of less than 10 millimeters or less than 5 millimeters, and particles carrying oleophilic materials with low weight percentages of solid, particulate-supporting material, and particularly particles functioning as high oleophilic content organogels.
2. Background of the Art
It is often desirable to provide materials into general media or onto surfaces in particulate form. Particles also provide a very efficient method of adding concentrations of physical or chemical additives into diverse systems. Typical vehicles for these types of additions include solid homogeneous particles of material, microcapsules, bubbles, beads, ground particulates, uniform particulates, and the like.
U.S. Pat. No. 6,270,836 describes microcapsules coated with a gel, specifically a gel produced by the sol-gel process. The gel coating provides certain resistances to the microcapsules, resulting in enhanced protection for their contents.
Microcapsules containing different types of materials are known, as are microencapsulation techniques to prepare such materials, which are used as starting materials in the process of this invention. Microcapsules can be used in many applications in which materials are to be contained either indefinitely or temporarily.
Microcapsules have been designed to allow the slow release of pharmaceutical preparations, cosmetic products and food products such as flavoring agents. The microcapsules used in the present invention on the other hand, are adapted to contain materials that interact indirectly with the environments in which they are used. Microcapsules are prepared according to known procedures. The material which makes up the microcapsule wall can be chosen from a wide variety of materials. The choice of materials depends primarily on the physical and chemical characteristics of the contents, and on the intended use of the microcapsules. The microcapsules should also be readily coatable with the metal oxide gel.
Preferred microcapsule forming materials include various thermoplastic materials, such as natural or synthetic fatty alcohols, fatty acids, fatty esters and waxes. Natural waxes include the vegetable waxes such as carnuba, cauassu, candelilla, farria, palm, esparto, sugar cane and cotton waxes; animal waxes such as beeswax, ghedda, chinese insect, shellac, spermaceti and lanolin waxes; and mineral wax such as paraffin, microcrystalline, ozokerite, montan and syncera waxes. Synthetic and modified waxes useful as microcapsule forming materials include the Carbowaxes, Abril waxes, Armid and Armowaxes (Armour & Co.) and Chlorax chlorinated paraffin wax (Watford Chemical Co.). It will be appreciated that waxes are a mixture of various components, and that each type of wax is itself available in a number of different grades. Other thermoplastic materials are described as useful as microcapsule wall-forming materials, including polyethylenes such as POLYWAX™ from Petrolite, Inc. (actually it is a polyoxyethylene polymer), polypropylenes, polyesters, polyvinyl chlorides, tristarch acetates, polyethylene oxides, polypropylene oxides, polyvinylidene chloride or fluoride, polyvinyl alcohols, polyvinyl acetates, polyacrylates, polymethacrylates, vinyl functional polymers, urethanes, polycarbonates, and polylactones. Further details on microencapsulation are found in U.S. Pat. Nos. 5,589,194 and 5,433,953.
A colloid is a suspension in which the dispersed phase is not affected by gravitational forces, due to the dimensions of the dispersed phase (1-1000 nm). A sol is a colloidal suspension of solid particles in a liquid. A gel can be considered to be the agglomeration of these particles into a structure of macroscopic dimensions, such that it extends throughout the solution. It is therefore, a substance that contains a continuous solid skeleton enclosing a continuous liquid phase. Generally, chemical processing of the gel precursors involves hydrolysis and condensation reactions in which the ligands of the precursors are replaced by bonds to the ligands of other metal or metalloid elements. This process results in a growing network of metal or metalloid elements linked together, eventually forming a gel.
Gelatin is an animal-derived protein that finds a wide array of food, pharmaceutical, photographic, and technical applications. It has been used to manufacture various types of capsules for more than a hundred years, and those capsules have been utilized in a wide variety of industrial and commercial applications. Softgels (soft gelatin capsules) are a common dosage form for the administration of liquid, semi-solid and solid fills, and soft gelatin capsules embody a distinct classification of properties within the gelatin art. The typical softgel manufacturing process uses the rotary die encapsulation system, and such a general manufacturing process is described by Wilkinson, P. K. and Hom, F. S., 1990, “Softgels: manufacturing considerations.” In: Specialized Drug Delivery Systems, P. Tyle (Ed.), pp. 409-449, Marcel Dekker, Inc., New York.
The primary components of the conventional capsule shell are gelatin, plasticizers and water. Several other minor shell additives may be present, such as coloring, opacifying, flavoring and antimicrobial agents. Extenders have been used in gelatin shell compositions to reduce the cost of materials within the shell and adjust the physical or chemical properties of the shell. Gelatin is manufactured by controlled hydrolysis of collagen, which is present in the bones, skins, and white connective tissues of animals. Gelatin obtained from acid hydrolysis of collagen is known as Type A gelatin, whereas gelatin obtained from alkali hydrolysis of collagen is known as Type B gelatin. Commercially, the primary raw materials for gelatin manufacturing are pigskins, and bones and skins from bovine animals. The softgel industry mainly uses gelatin derived from bovine bones.
U.S. Pat. No. 3,959,540 discloses an outer coating made of an acrylic polymer that renders softgels resistant to gastric juices and suitable for enteric release. The gelatin capsules comprise three layers: an inner gelatin shell, an intermediate layer comprising a cationic polymerizate of di-lower alkylamino lower alkylmethacrylate, and outer gastric juice resistant coating of an anionic polymerizate of methacrylic acid and acrylic acid esters.
Coating of softgel capsules with an acrylic film that possesses enteric release properties also is discussed by Felton, L. A., Shah, N. H., Zhang, G., Infeld, M. H., Malick, A. W. and McGinity, J. W. 1996. “Physical-mechanical properties of film-coated soft gelatin capsules.” International Journal of Pharmaceutics, 127:203-211. The article describes that storage at low relative humidity causes an increase in the Young's Modulus for the capsules over time.
U.S. Pat. No. 4,816,259 discloses the application of a hydroxypropyl methylcellulose subcoating to the outer surface of a softgel. This subcoating improves the mechanical strength of the capsule and the capsule surface adheres better to known enteric coating compositions.
U.S. Pat. No. 4,350,679 discloses the application of a carnauba wax coating on a softgel. The functionality of the wax coating is to improve shell strength and moisture resistance.
U.S. Pat. No. 4,055,554 discloses the use of chemically modified dialdehyde polysaccharides as gel strength enhancers for gelatin compositions. Such compositions may be used for manufacturing capsules.
U.S. Pat. No. 4,804,542 discloses a softgel wherein the capsule shell contains (at least 1% by weight) an additive capable of absorbing water in an amount of at least 10% by weight of its own weight. Such additives include starches, starch derivatives, celluloses, cellulose derivatives, and milk powder. Some non-hygroscopic materials such as mono-, di-, and oligosacchrides, lactose, magnesium trisilicate, and colloidal silica also are described as useful.
U.S. Pat. No. 5,554,385 discloses a softgel wherein the dry capsule shell is comprised of 3-60% starch having a high amylose content. This invention involves preparation of gel mass by combining gelatin, high amylose starch, plasticizers, water, and other minor additives. The gel mass is then processed with the rotary die encapsulation machine to manufacture softgels. The capsules of this invention have textured frosted or satin finish. Microcapsules incorporating a flavor or fragrance compound are useful to provide a controlled release of the contained flavor or fragrance. Such products may be used in the food processing industry, where encapsulated flavor particles may provide a flavor burst upon chewing the food or may allow taste evaluation of a botanical or food/beverage aroma. Such products may also be used in the cosmetic and toiletry industries, where encapsulated fragrance particles may provide a burst of scent upon capsule fracture. The capsule may comprise a shell surrounding a core material in which the flavor or fragrance compound is contained.
Microcapsules may be formed by a coacervation or crosslinking process, in which lipids are coated by tiny droplets of proteins, carbohydrates, or synthetic polymers suspended in water. The process of coacervation is, however, difficult to control and depends on variables such as temperature, pH, agitation of the materials, and the inherent variability introduced by a natural protein or carbohydrate.
In the manufacture of microcapsules containing a flavor or fragrance compound, several features are desirable. It is desirable to produce microcapsules that have strong walls and that do not agglomerate. It is desirable that the compound be readily loaded into an oil microparticle, that is, be readily absorbed into the oil core of the microcapsule. Once absorbed, it is also desirable that the compound be irreversibly retained in the oil core of the microcapsule, that is, be adsorbed into the microcapsule.
The amount of compound that may be encapsulated depends upon several factors including its solubility in a fluid such as a gas or water, partition coefficient, molecular weight, water content, volatility, and the ratio of blank capsule to water amounts. Flavors and fragrances may be mixtures of hundreds of components, each of which may vary widely in these properties. A flavor or fragrance compound that is lipophilic may be readily contained in an oil core of a microcapsule, while a flavor or fragrance compound that is hydrophilic may be less readily contained in an oil core. For example, the flavor compound diacetyl (DA) is about 20% to about 30% water-soluble. For diacetyl, typical maximum absorption into an oil is up to only about 55%. A highly water-soluble compound such as diacetyl is also more difficult to retain in the oil core once it is loaded.
A compound's solubility in an aqueous phase versus an oil phase is determined by its partition coefficient, abbreviated as K. The partition coefficient of a compound is the ratio of the compound's concentration in one liquid phase to the compound's concentration in another liquid phase (Kliquid/liquid) or in one gaseous phase to another liquid phase (Kgas/liquid). The partition coefficient thus is an inherent property of the compound with two given liquid phases, such as a lipid phase and an aqueous phase, or a lipid and a gas phase, and reflects the compound's distribution at equilibrium between the water or gas phase and the lipid phase. Any means of decreasing the water solubility of a compound will shift the equilibrium of the compound and thus shift its partitioning between an aqueous or gas phase and a lipid phase. For example, addition of a salt will decrease the water solubility of a compound and will increase its partitioning into the lipid phase. Similarly, crosslinking a protein membrane to strengthen the membrane and physically decrease the amount of water, or physically removing water from the environment, causing capsule wall or membrane shrinking, will decrease the water solubility of a compound and will increase its partitioning into the oil phase.
Flavors or fragrances that are water soluble may interfere with encapsulation of an oil particle. For example, flavor or fragrance compounds that are water soluble cannot be encapsulated using gelatin coacervation. This is because for coacervation to occur, there must be a droplet to coat, and for these water soluble materials, there are no droplets to coat. In addition, the water soluble flavor or fragrance may partition so as to locate the flavor or fragrance compound in an aqueous environment outside the encapsulated oil particle rather than inside the oil particle. If a flavor or fragrance compound is too water soluble, the coacervation process ceases to function due to the colloid becoming either too thick or too thin. A colloid that is too thick has no flow, and thus cannot properly coat the oil surface. A colloid that is too thin is not retained on the oil surface. In the extreme, a water-soluble flavor or fragrance compound can totally solubilize the colloid, leaving no wall material to deposit on the oil surface.
Besides water solubility, a flavor or fragrance compound that contains fatty acids affects the pH of a coacervation reaction. If a base is added in an attempt to adjust pH, the fatty salts produced in the reaction impart an undesirable soap taste to a flavor compound. If a flavor or fragrance compound contains water-soluble esters, the coacervation temperature is affected and hence the final gelation temperature is altered. While it is therefore desirable to limit compounds that contain either fatty acids or water-soluble esters, there is a tradeoff in the potency and profile results for the encapsulated compound. This limits the range of formulations that are able to be effectively encapsulated.
U.S. Pat. No. 6,103,269 describes an active compound-containing powder, granule or pellet, comprising a dispersion of at least one active compound or active compound having poor absorbability in vivo in a matrix which essentially includes a structure-forming agent comprising hydrophilic macromolecules which are selected from the group consisting of collagen, gelatin, fractionated gelatin, collagen hydrolyzates, succinylated gelatin, plant proteins, plant protein hydrolyzates, elastin hydrolyzates, and mixtures thereof, which is prepared by a process that comprises the step of: a) dissolving a structure-forming agent comprising hydrophilic macromolecules selected from the group consisting of collagen, gelatin, fractionated gelatin, collagen hydrolyzates, succinylated gelatin, plant proteins, plant protein hydrolyzates, elastin hydrolyzates, in an aqueous or aqueous-organic solvent; b) dispersing the active compound and c) adding the mixture of dissolved structure-forming agent and dispersed active compound dropwise to a deeply-cooled, easily evaporable liquid and thus forming powders, granules or pellets, and d) drying the powders, granules or pellets thus formed by evaporation or sublimation of the solvent in a customary manner until the solvent is removed.
U.S. Pat. No. 6,066,613 describes large hydrogel particles suspended in an aqueous medium and to a continuous extrusion/mixing process for making this kind of hydrogel particles. The hydrogel particles comprise two different high molecular weight polymers. One is insoluble in the said aqueous medium and is used for network formation and gel integrity. The other is soluble in the said aqueous medium and helps control gel swellability and gel strength. Water insoluble materials are entrapped or encapsulated inside the network formed by these two polymers and are able to be more efficiently delivered from the aqueous composition (e.g., liquid cleanser containing the hydrogel particles). Gel particles with controllable size and controllable gel strength are prepared simply by first adding (e.g., injecting) an aqueous solution containing the said two polymers and the water insoluble material into the said aqueous medium to form elongated soft polymer gel noodles; and the noodles are then cut/broken (e.g., through mixing or mechanical agitation) into desirable gel particle size. These hydrogel particles are synthesized and supported in the aqueous medium.